Soil soluble sulphates

Hello there!

I Have read your national standard 2720 part 27 in which are presented different methods for determination of sulphates .

I am interesed about the Volumetric Method in which ia presented a formula for the calculation of the sulphates:
I wish to know how the term 0.0177 was determinated or what does IT represent¿???

Thank You în advance!!?